title: Structural basis for the exclusive specificity of Slac2-a/melanophilin for the Rab27 GTPases.
abstract: Rab27A is required for actin-based melanosome transport in mammalian skin melanocytes through its interaction with a specific effector, Slac2-a/melanophilin. Mutations that disrupt the Rab27A/Slac2-a interaction cause human Griscelli syndrome. The other Rab27 isoform, Rab27B, also binds all of the known effectors of Rab27A. In this study, we determined the crystal structure of the constitutively active form of Rab27B complexed with GTP and the effector domain of Slac2-a. The Rab27B/Slac2-a complex exhibits several intermolecular hydrogen bonds that were not observed in the previously reported Rab3A/rabphilin complex. A Rab27A mutation that disrupts one of the specific hydrogen bonds with Slac2-a resulted in the dramatic reduction of Slac2-a binding activity. Furthermore, we generated a Rab3A mutant that acquires Slac2-a binding ability by transplanting four Rab27-specific residues into Rab3A. These findings provide the structural basis for the exclusive association of Slac2-a with the Rab27 subfamily, whereas rabphilin binds several subfamilies, including Rab3 and Rab27.
authors.affiliation: Systems and Structural Biology Center, Yokohama Institute, RIKEN, 1-7-22 Suehiro-cho, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Mutsuko
authors.initials: M
authors.lastname: Kukimoto-Niino
authors.forename: Ayako
authors.initials: A
authors.lastname: Sakamoto
authors.forename: Eiko
authors.initials: E
authors.lastname: Kanno
authors.forename: Kyoko
authors.initials: K
authors.lastname: Hanawa-Suetsugu
authors.forename: Takaho
authors.initials: T
authors.lastname: Terada
authors.forename: Mikako
authors.initials: M
authors.lastname: Shirouzu
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D025941:Protein Interaction Mapping; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C435724:Mlph protein, mouse; C512958:Rab27b protein, mouse; D020691:rab GTP-Binding Proteins